Short wave reception



Patented July 28, 1931 HOLLIS s. :BAIBD, or BOSTON,massncnnsnrcrsessmnon 'ro'snoa'rwavn ,&ITELE- VISION CORPORATION, OFBOSTON, MASSACHUSETTS, A CORPORATION OF DELA- WARE SHORT WAVE nncnrrionApplication filed April 30, 19 29 Serial No. 359,268.

This invention relates to apparatus and systems for the reception ofradio signals and has particular relation to the reception of short wavesignals.

It is well known that the tuning range of a radio receiving apparatus islimited to a certain band or range of wave lengths and can noteffectively receive signals that are outside its band without a changeof tuning apparatus, as inductances or condensers. re-

ceiverdesigned to operate on the so-called broadcast band or on waves ofbetween 200 and 550 meters cannot receive signals which are transmittedon much shorter wave lengths as, for instance, or meters. I haveprovided an arrangement whereby the usual receiver may-be adapted forthe reception of signals, and especially short wave signals that areoutside its normal operating range. To 20 this end, I provide a shortwave adaptor set having a detector tube and tuning apparatus for theshort waves, with aterminal plug adapted removably to enterthedetectortube socket of the long :wave receiver and connect the outputof the adaptor setlwith the source of plate supply and the audiofrequency amplyfying stage of the long wave set. In this manner. thebroadcasting receiver may be arranged for the reception of signal transmitted on the shorter waves without any other changes than the removalof the detector tube of the long wave receiver and the insertion of theadapter plug in the detector tube socket.

It is common to heat the cathodes or fila- 1 ments of the tubes ofreceiving apparatus by alternating current supplied directly from'astep-down transformer energized from the alternating current lightingmains. This method is quite satisfactory for the reception of signalswithin or above the present broad- .cast band of'wave lengths. however,that when it is attempted to heat the cathode of the detector tube'ofthe short wave adaptor set from the same source of alter.- natingcurrent that supplies thebroadcasting receiver, the alternating currentproduces such a loudaudio frequency note as seriously to interfere withthe intelligible reception of signals on the shorter waves.

an object ofthe present invention to provide I have found,

It is therefore a short wave adaptor set or converter 7 for broadcast orlong wave receivers wherein the anode circuit of the detector tube ofthe short wave adaptor set is supplied with power from the correspondingpower source of the long wave set and'wherein the cathode of thedetector tube is energized by a direct current source of power as abattery that is an inherent part of the adaptor set and isentirelyindependent of the source of filament or cathode heating of thelong wave receiver.

A further object of the invention is the combination of a multi-tubelong wave receiver having its cathodes heated from a source ofalternating current and a short wave receiver connected "removably intoa portion of the long wave receiver and having the cathode of itsdetector tubeheated by a source of direct current and its anode circuitenergized by the anode power for the long wave receiver.

A further object of the-invention is generally of signals on shortwaves;

Fig. 1 is a diagrammatic and simplified representation of a radioreceiver adapted for operation on long waves combined with a short waveadaptor therefor arranged in ac- V cord ance with the present invention.

Fig. 2 is a perspective view of the short waveadaptor set having theshort wave circuitofFigl.

Fig. 3 is a plan view of the detector tube socket of the long wavereceiver of Fig. 1.

The long wave receiver illustrated dia-- gra'mmaticallyin Fig. 1, whichis adapted to receive over the broadcasting band of wave lengths, is ofa more or less conventional type and includes the two radio frequencyamplito improve the construction and operation of apparatus adapted forthe reception I fying-stages v10and 12, the detector stage 14,

and the two audio frequency amplifying steps 16 and 18, the outputcircuit of the last stage of which operates a load device 20 which maybe a loud speaker orthe like. A collection agency as the antenna A iscoupled with the input circuit of the first stage. 'The anode or plate22 of the detector tube is coupled" through a suitable audio frequencytranslating device as the transformerQ iwith the grid of the nextsucceeding stage as is more or less usual practice. The grid 26 of thedetector tube is energized from the plate or output circuit of theproceeding radio frequency stage as is also usual practice.

The filaments or cathodes 28 of the amplifying stages are supplied withalternating current by the low tension winding 30 of a step-downtransformer 32 the primary 34 of whichis connected to the higher tensionalternaiing current mains 35. The grid circuits 36 of said amplifyingtubes are connected by means of a conductor 38 with a mid-point of saidlow tension primary winding or a point of invariable potential, wherebytominimize the effect of the alternating current in the filaments in theoutput circuits of the tubes. Theanodes of the tubes are supplied with ahigh "tension direct current by a suitable source 39 which is energizedfrom the high tension alternating current mains 35.

' The detector tube is provided with a heater 40 which heatsa cathode42, the heat storage capacity of which is sufficient to maintain areasonably uniform rate of ion emission so that the alternations ofcurrent in the heat ing circuit do not have an unduly pronounced effectin the output circuit when the receiver isoperating on long waves. Ashas been stated above, however, this type of tube is unsatisfactory forthe reception of shorter Waves, because of the magnification of theeffect of the fluctuations in temperature of the cathodes, when the tubeis used as a detector for short wave signals.

The short wave adaptor, which is used to enable the long wave receiverabove described to receive signals transmitted on shorter waves as on 20and 40 meters, is separate from the long wave receiver and is containedin a separate case 44, see Fig. 2.

' The short wave adaptor includes a detector tube 46 havin the grid 48,the anode or plate 50 and the fi aments 52, which, preferably, has a lowpower consumption. The grid circuit of the tube includes a fixedinductance 54 anda tuning condenser 56. The grid circuit is connected tothe antenna A of the long wave receiver by a coupling condenser 58. Thecircuit here shown is of the regenerative type and includes a fixed feedback winding which is in inductive relation with the inductance 54 andis carried on the same form 55 therewith and is provided with aregeneration control condenser 62 in series therewith to controlregeneration'and volume of the signal in the audio frequency outputcircuit 64 of the tube. The output circuit 64 includes two conductors,one extending from the plate 50 and the other from the filament 52. Theplate condenser has a'choke coil 65 therein by which to keep thehighfrequency current out of the audio frequency circuit. Thetypeofituning and regeneration circuits is of no particular consequence sofar as this invention is concerned although the circuit herein shownworks excellently in practice. The conductors of the output circuit 64are flexible and terminate in a plug 66 where they are connected toprongs 222; and 427), respectively. The plug is also provided with otherprongs 68 which are not connected with any circuit but which are for thepurpose of centering the plug and holding it in the socket of thedeflector tube of the long wave re ceiver.

The detector tube socket of the long wave receiver is illustrated inFig. 4 and has the grid and plate terminals 26a and 22a respectively,the cathode terminal 42a and the heater terminals 40a with which thecorresponding elements of the detector tube of the long wave receiverare adapted to be con nected when the tube is in the socket. .In the useof the short wave adaptor, the detector tube is adapted to be removedand replaced by the plug 66. The prongs 22b and 42b of the plug areadapted to engage the terminals 22a and 42a of the socket whereby to beconnected with the plate and cathode circuits respectively of thedetector, thereby to be energized from the anode power source 39 of thelong wave receiver and to feed the audio frequency signals received, bythe detector set into the audio frequency stages of the long wavereceiver.

In accordance with this invention, the short wave detector tube 46 hasits filament supplied by a self-contained direct current source of power7 0 that is located in a lower portion of the enclosing case 44 of Fig.2. Thus, the filament 52 of the short wave detector tube is entirelyindependent from the alternating current source of energy for the tubesof'the long wave receiver and consequently' the signal from the adaptoris free from any alternating current hum. The long wave receiver can.thus deliver a clear signal that is transmitted on a short wave.

I claim:

1. The combination of a long wave multistage radio receiver having aplurality of tubes and a source of alternating current power for heatingthe cathodes of said'tubes, and a short wave adapter for said long wavereceiver having a detector tube, an input circuit tuneable to the shortwaves, an output circuit having a detachable connection with anintermediate stage of said long wave receiver and having a directcurrent source of power for heating the cathode of said detector tubeindependently of the source of alternating current power.

2. The combination of a long wave radio receiver having a plurality ofamplifying stages and a detector stage having plate and cathodecircuits, each stage having a thermionic tube associated therewith, asource of alternating current power for heating the cathode of'saidtubes, a short wave adaptor receiver having amplifying and detector andcathode circuits, for said stages, said a tube socket that has ed by thedetector stages including plate and thermionic tubes detector stagehaving plate and cathode terminals enga corresponding terminals of saitensiondirect current for heatingthecathode of said short wave detectortube, which source is independent of said source of alternating currentof said long wave receiver.

In testlmony whereof, I have signed my name to this specification.

HOLLIS S. BAIRD.

tube and connected with the plate and cathode circuits of said stage, asource of alternating current power for heating the cathodes of saidtubes, a short wave adaptor including a detector tube having an inputcircuit tuneable to the short waves and having output and cathodeconductors connected respectively to the plate and to the cathode ofsaid detector tube, a plug having prongs connected to said conductorsadapted to be received in the detector tube socket of said long wavereceiver and to engage respectively the plate and cathode terminals ofsaid sockets,-and a source of direct current power for heating thecathode of said adaptor detector tube, said source of direct currentpower being connected directly to the cathode of said detector tube andbeingindependent of the source of alternating current of said long wavereceiver and also independent of said output and cathode conductors.

4. In a long wave radio receiver having'a thermionic detector tube thecathode of which is heated by alternating current, the method ofadapting said receiver for the reception of short wave signals whichconsists in providing a separate detector tube,

supplying the input circuit of said separate detector tube with a tunedshort wave signal,

, heating the cathode of said tube by direct current, and feeding theoutput of said tube into the output of the detector tube of the longwave receiver.

5. The combination of a long wave multistage radio receiver having aplurality of I amplifying and detector tubes, a source of alternatingcurrent for heating the cathodes of said tubes, a source of high tensiondirect current power for supplying the anodes of said tubes,-and a shortwave adaptor for said having a detector tube, an input circuit therefortuneable to the short waves, means for connecting the cathode and anodeof said short wave detector tube removably with the cathode and anodecircuits of said long wave detector tube, whereby also to connect theanode of said short wave detector tube with said source of high tensiondirect current power, and a source of low

